I've successfully built this VCO circuit using an LM13700 that works just fine if the VC (the 510K resistor) is not connected to anything. Needless to say, I'd like to be able to change the frequency of this VCO. However, when it's connected to a voltage source (potentiometer) it doesn't change the frequency but the amplitude. Tweaking the pot just makes the signal 'die'. I suspect the equations at the bottom has a lot to do with the frequency but I just cannot decipher them. What am I doing wrong? How can I change the pitch?